Missouri Pest Monitoring NetworkSpotted Wing Drosophila I.D.

Identification of fly(stage attracted to and captured in traps)

Female flies (right) have a prominent, serrated and saw-like egg-laying device on their hind end that inserts eggs into ripe fruit.

Adult male flies have a black spot near the leading edge of each wing tip and have two sets of black combs, which appear as bands on their front legs.

Both SWD and the common vinegar fly have red eyes and an amber-colored body. Careful examination is needed to prevent confusing SWD with common vinegar flies. It is highly advisable to use a 30X magnifying glass, small hand lens or head-mounted magnifier to more easily see the key characteristics described above. Being able to look at flies under a stereomicroscope will greatly aid in ability to accurately ID female SWD.

Field Scouting

Because SWD reproduces so quickly under optimum conditions, the first catch information is vital to activate pest management programs to prevent rapid population increases and potential infestations on a farm. Monitoring helps us to detect the earliest populations of SWD and to determine when populations are likely to cause the most damage.

How to Field-Scout for Spotted Wing Drosophila:

An IPM program for SWD includes the use of monitoring traps to assess adult population levels throughout the harvest season.

BAIT

A simple and effective monitoring trap can be constructed using plastic containers baited with a solution made of active dry yeastÂ (Â½ tablespoon), standard white granulated table sugar (2 tablespoons), and water (preferably warm; 6 ounces). Recently, some synthetic lures became commercially available.

If possible, prepare the yeast mixture 24 hours before placing (or servicing) the traps in the field to increase fermentation and bait attractiveness to SWD.

TRAPPING

SWD will multiply first on wild fruit (raspberries or blackberries in hedgerows, mulberries, wild cherries, etc.). Start trapping as soon as fruit on the wild host begin to turn color, and continue until final harvest of fruit crop.

Place one monitoring trap every 2-3 acres on wild host (Washington State Univ. recommends 1 trap in each crop or 1 trap per acre for large plantings). Whenever possible, locate a mulberry tree, in close proximity to the fruit crop.

Once the crop ripens to a susceptible stage (first color change), move the trap from the wild host to the fruit crop.

Traps for SWD are best placed in the shade and in the fruit zone. For strawberries this is on the ground, whereas for bush fruit or tree fruit, the trap needs to be hung up at about 3-4 ft., on the most shaded / coolest side of the plant canopy. Make sure holes are exposed and not blocked by vegetation.

Traps should be serviced once a week. At every inspection date, bring a trap already baited with 24-hour old bait and just replace the ‘old’ baited trap with this newly baited trap.

IDentification

Dump the contents of the trap that was removed from the field into a strainer and rinse off with tap water.

The sugar/ yeast bait will attract a large number of non-target insects that are able to enter the trap through the small holes. Eliminate non-target insects i.e., insects that are much larger than Drosophila or are not the correct color.

Examine the remaining insects under 30x magnifier to look for spots on wings (males), 2 dark bands on front legs (males), or dark teeth on ovipositor (females). Seeing the female’s serrated ovipositor with a hand lens is possible, but being able to look at flies under a stereomicroscope, which are available for purchase online, will greatly aid in ability to accurately count female flies.

MANAGEMENT

So far no economic thresholds for SWD have been developed, so several universities are currently recommending a conservative approach in which capture of one or more SWD on a given farm triggers insecticide application if fruit crops are at a susceptible stage. Protection of fruit needs to take place through to harvest using registered insecticides.